The Institute of Electrical and Electronics Engineers (IEEE) Standard 802.3ae, entitled “Ten Gigabit Per Second Ethernet Task Force” defines a gigabit per second industry standard for interconnecting high-performance switches, routers, servers, and the like in the backbone of local area networks (LANS), Metropolitan Area Networks (MANs), native attachments to a Wide Area Network (WAN), and the like. Two features specified by the 802.3ae standard are a 32-bit data path and a clock. In operation, the 32-bit data and clock are received by a physical layer device and forwarded through a Media Independent Interface (MII) to a Media Access Controller (MAC).
The MAC resides on the data path between the Physical Layer Controller (PHY) and a Packet Switching Controller (PSC). In accordance with industry standards a MAC is required to support certain standardized features and functions. However, MAC designers often have flexibility, to determine how to support the standardized functions and features.
Data transmission speed across the data path is generally a product of the data path width and the data sampling speed. In addition, the clock frequency of a data transmission system is inversely proportional to the data path width if the same total aggregate throughput is to be maintained in a pipelined system. It is known to implement Ethernet MAC layer logic as a pair of same bit width receive and transmit data paths to which operations are performed. As such, it then follows that the same size receive and transmit data paths in a MAC application will require the same clock frequencies for each path.
For the transmit data path, the desired clock frequency is easily generated by an external commercial oscillator. For the receive data path, however, the receive clock is derived from the IEEE specified MII receive data clock. The specified MII-supplied clock frequency, however, is inadequate to maintain certain data rates such as, for example, a 10 Gbps data transmission rate, using rising edge only sampling of 32-bit wide data. In fact, the MII-supplied receive clock specified by the IEEE standard is approximately half the frequency required to generate the 32 bit data path as desirable at a 10 Gbps data rate on the transmit side.
The deficiencies of present methods for maintaining data throughput at high data rates show that a need exists for maintaining high data throughput in a data element compatible with standardized features specified by IEEE 802.3ae.